I'm walking right up to the crowd now to see ........

When asking about what has occurred, the correct form is 'what's happened' (what has happened). This uses the present perfect tense for recent events with current relevance. Option B is correct. 'What's happen' and 'what's happens' are grammatically incorrect. 'Occurring' is misspelled (should be 'occurring') and present continuous doesn't fit the context.